Weeds are plants that compete with cultivated plants in an agronomic environment and cost farmers billions of dollars annually in crop losses and the expense of efforts to keep weeds under control. Weeds also serve as hosts for crop diseases and insect pests. The losses caused by weeds in agricultural production environments include decreases in crop yield, reduced crop quality, increased irrigation costs, increased harvesting costs, reduced land value, injury to livestock, and crop damage from insects and diseases harbored by the weeds. The principal means by which weeds cause these effects are: 1) competing with crop plants for water, nutrients, sunlight and other essentials for growth and development, 2) production of toxic or irritant chemicals that cause human or animal health problem, 3) production of immense quantities of seed or vegetative reproductive parts or both that contaminate agricultural products and perpetuate the species in agricultural lands, and 4) production on agricultural and nonagricultural lands of vast amounts of vegetation that must be disposed of. Herbicide tolerant weeds are a problem with nearly all herbicides in use, there is a need to effectively manage these weeds. There are over 365 weed biotypes currently identified as being herbicide resistant to one or more herbicides by the Herbicide Resistance Action Committee (HRAC), the North American Herbicide Resistance Action Committee (NAHRAC), and the Weed Science Society of America (WSSA).
The Acetyl-CoA carboxylase (ACCase) enzyme catalyzes the biotin-dependent carboxylation of acetyl-CoA to produce malonyl-CoA, this is the first and the committed step in the biosynthesis of long-chain fatty acids. This enzyme is the target of many herbicides that include members of the chemical families of aryloxyphenoxypropionates, cyclohexanediones and phenylpyrazoline.